A known method of producing a rare earth magnet powder which is excellent in magnetic anisotropy includes mixing a rare earth magnet alloy raw material hydride powder having a chemical composition which includes, in atom % (hereinafter % represents atom %), one, or two or more rare earth element including Y: 10 to 20%, Co: 0 to 50%, B: 3 to 20%, and M: 0 to 5% (wherein M represents one, or two or more from among Ga, Zr, Nb, Mo, Hf, Ta, W, Ni, Al, Ti, V, Cu, Cr, Ge, C, and Si), with the balance including Fe and inevitable impurities, and a powder including Dy and Tb in an elemental, alloy, or compound form, or in hydrides thereof (an elemental, alloy, or compound form) so as to produce a mixed powder; diffusion heat-treating the mixed powder; and then carrying out hydrogen absorption of the diffusion heat-treated mixed powder.
The aforementioned rare earth magnet alloy raw material hydride powder is produced by the following known method: carrying out hydrogen absorption by heating, or heating and holding a rare earth magnet alloy raw material from room temperature to a temperature below 500° C. in a hydrogen atmosphere; carrying out hydrogen absorption-decomposition by heating and holding the rare earth magnet alloy raw material at a predetermined temperature in a range of 500 to 1,000° C. in a hydrogen atmosphere with a pressure of 10 to 1,000 kPa so as to induce the rare earth magnet alloy raw material to absorb hydrogen and to be decomposed due to a phase transformation; carrying out heat treatment in depressurized hydrogen with some hydrogen remaining in the rare earth magnet alloy raw material by holding the rare earth magnet alloy raw material subjected to the hydrogen absorption-decomposition at a predetermined temperature in a range of 500 to 1,000° C. in a hydrogen atmosphere with an absolute pressure of at least 0.65 but less than 10 kPa or in a mixed hydrogen/inert gas atmosphere with a hydrogen partial pressure of at least 0.65 but less than 10 kPa; and then cooling the rare earth magnet alloy raw material to room temperature by introducing Ar gas (see Patent document 1: Japanese Patent Application, First Publication No. 2002-93610).
Also, in the case of producing a magnetically anisotropic HDDR magnet powder that is the aforementioned rare earth magnet powder, the following method is used: carrying out hydrogen absorption for a rare earth magnet alloy raw material; carrying out hydrogen absorption-decomposition by heating and holding the rare earth magnet alloy raw material at a predetermined temperature in a range of 500 to 1,000° C. in a hydrogen atmosphere with a pressure of 10 to 1,000 kPa so as to induce the rare earth magnet alloy raw material to absorb hydrogen and to be decomposed due to a phase transformation; and then carrying out hydrogen desorption by holding the rare earth magnet alloy raw material subjected to the hydrogen absorption at a predetermined temperature in a range of 500 to 1,000° C. in vacuum. Accordingly, the magnet obtained by the aforementioned method is known to have a recrystallization texture in which recrystallized grains, whose main phase is a R2Fe14B intermetallic compound phase that is substantially a tetragonal structure, are adjacent to each other, and the recrystallization texture includes a basic texture of a magnetically anisotropic HDDR magnet powder in which the recrystallized rains, whose ratio (b/a) of a longest particle diameter (b) to a shortest particle diameter (a) is less than 2, exists at 50 vol % or more of all the recrystallized grains and an average recrystallized grain diameter of the recrystallized grains is 0.05 to 5 μm (see Patent document 2: Japanese Patent No. 2576672).
Recently, in the electrical and electronics industries, a need has arisen for a rare earth magnet powder which is further excellent in magnetic anisotropy. In the automotive industry in particular, active development work is being carried out on electric vehicles, including the motors to be mounted in such vehicles. The motors that are mounted in such electric vehicles are sometimes installed close to a small gasoline engine or left out under the scorching sun, so it is not unusual for them to be placed in an environment where they are particularly subjected to heating. Accordingly, there exists a need for a rare earth magnet powder which is so excellent in thermal stability and magnetic anisotropy including both coercivity and remanence that it can be used to produce motor components which is further excellent in heat resistance and magnetic properties.